A small (or big) fan goes a long way to allow one to sleep without dripping in a tent in the Sunny Summery South. A car battery will last for quite a while. Without a fan its pretty miserable... and then there are the sandflies that crawl thru the mosquito screen and bite! Big Sailboat sleeping is helped with a fan too. Take a ccoooool bath first and get all de-sweaty.
I tried this in an old van once: not only had there been a large old hound dog sleeping on its shag carpet, but the big V8 engine was hot and took HOURS to cool of, and every one of its BTUs went directly into my body. NO FAN EITHER. Awful <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />- a 22 hour night.